Surface-mount air-core coil, electronic component having the same, and communication apparatus having the same

ABSTRACT

A surface-mount air-core coil has a coil body formed by winding a conductive wire spirally and mount legs formed by folding both ends of the conductive wire horizontally toward the inside. The lower surfaces of the mount legs are positioned below the lower surface of the coil body. The length of the mount legs is set longer than the width of the coil body.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a surface-mount air-core coil mainlyserving as an inductor for use at a high frequency, an electroniccomponent having the air-core coil, and a communication apparatus havingthe air-core coil.

2. Description of the Related Art

A surface-mount air-core coil disclosed in the Japanese Examined UtilityModel Publication No. 5-39611 has been known. As shown in FIG. 12 andFIG. 13, the air-core coil 80 has a coil body 82 formed by winding aconductive wire 81 spirally except for both ends thereof and mount legs83 formed by folding both ends toward the inside at right angles. Thecoil body 82 has a circular shape and the lower surface 82a thereof ispositioned on the same surface as the lower surfaces 83a of the mountlegs 83. Therefore, the height H and the width L of the air-core coil 80is equal to the outer diameter of the coil body 82. The horizontallength L₁ of the mount legs 83 is shorter than the width L.

The air-core coil 80 is accommodated into each pocket 87 of a packagetape 86 as shown in FIG. 14 and supplied to a mounting line. Awithdrawing nozzle of a mounting machine (not shown) takes the air-corecoil out of each pocket and mounts it at the specified position on aboard 85.

When air-core coils having various characteristics, includinginductance, are manufactured, the air-core coils have minutely differentdiameters in the coil bodies and the height H and the width L of eachair-core coil become different. Since only one type of package tape 86is prepared to reduce manufacturing cost, a small air-core coil may behandled inappropriately with the pocket 87 having fixed dimensions. Inother words, if the coil is too small in height compared with the depthof the pocket 87, the coil may rotate in the pocket 87 and be turnedupside down, preventing mounting even if it is taken out. If the coil issmall in width compared with the width of the pocket 87, the coil maymove in the pocket 87. It becomes difficult to remove the coil, and inaddition, erroneous mounting may occur due to a change in position. Thisproblem can be eliminated by providing a package tape having a pocketsuited to the size of each type of air-core coil. However, this is anexpensive solution.

As shown in FIG. 13, in the conventional air-core coil 80, the lowersurface 82a of the coil body 82 is positioned ideally on the same planeas the lower surfaces 83a of the mount legs 83. Due to manufacturingerrors, however, the lower surfaces 82a and 83a are usually not on thesame plane. As shown in FIG. 15, for example, if the lower surface 82ais lower than the lower surfaces 83a, one or both of the mount legs 83may be improperly soldered to the circuit board 85. Alternatively, oneof the mount legs 83 may be soldered and the air-core coil stands on theboard 85, which is a so-called tombstone phenomenon. It is inconvenientfor the mount legs 83 to have a small length L₁ when soldered.

Furthermore, since the coil body 82 has a circular cross sectionperpendicular to its axis as shown in FIG. 12, when the coil has a largeinductance, it becomes large in diameter and the height H also becomeslarge.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide asurface-mount air-core coil having good mountability to a circuit board,an electronic component having this air-core coil, and a communicationapparatus having this air-core coil.

Another object of the present invention is to provide a surface-mountair-core coil which neither rotates nor moves in position whenaccommodated into a pocket of a package tape, an electronic componenthaving this air-core coil, and a communication apparatus having thisair-core coil.

Still another object of the present invention is to provide asurface-mount air-core coil which can have a low profile whilemaintaining the same characteristics, including inductance, anelectronic component having this air-core coil, and a communicationapparatus having this air-core coil.

The foregoing objects are achieved in one aspect of the presentinvention through the provision of a surface-mount

air coil formed of a single conductive wire and having a height and alength, said air coil comprising:

first and second substantially straight legs defined by opposite ends ofsaid conductive wire, each of said legs having a lowermost edge lying ina first plane; and

a cylindrical coil body defined by a spirally wound section of saidconductive wire, said coil body having a nominal diameter and a centralaxis lying parallel to and spaced from said first plane, said coil bodyhaving a height as measured between uppermost and lowermost outerperipheries of said coil body as viewed along a second plane runningperpendicular to said first plane and through said central axis, saidcoil body having a length as measured between leftmost and rightmostouter peripheries of said coil body as viewed along a third plane whichextends parallel to said first plane and through said central axis;

said lowermost outer periphery of said coil body being located above andspaced apart from said first plane whereby said height of said air coilas measured along said second plane is greater than said height of saidcoil body; and

each of said legs straddling opposite sides of said coil body as viewedalong said first plane such that said length of said air coil asmeasured along said first plane is greater than the length of said coilbody.

The surface-mount air-core coil having the above structure is soldered,for example, to a circuit board of an electronic component or acommunication apparatus by use of the mount legs. Since the mount legsare positioned below the coil body, the mount legs positively contactthe circuit board with the lower surface of the coil body not contactingthe circuit board even if the outer diameter of the coil body varies indimension. Problems, such as defective soldering, soldering prevention,and the tombstone phenomenon, do not occur. In addition, when the lengthof the mount legs is set longer than the width of the coil body,mountability is improved with the sufficiently long legs.

The height of an air-core coil according to the present invention isequal to the sum of the height (outer diameter) of the coil body and theoffset of the mount legs. By adjusting the offsets, coils havingdifferent outer diameters according to their characteristics, includinginductance, can be manufactured at the same height. Even with coilshaving different outer diameters, when the length of the mount legs isset to a fixed length which is longer than the widths (outer diameters)of the coil bodies, the coils have the same width irrespective of theouter diameters of the coil bodies. Therefore, coils having differentouter diameters can be manufactured with a height and a width which aresuited to the pockets of a package tape having fixed dimensions. Thecoils do not move or rotate in the pockets. In other words, when onetype of a package tape having pockets suited to a fixed height and afixed width of air-core coils is prepared, the air-core coils areprevented from rotating and moving in the pockets, positively allowingthe coils to be taken out by an automatic mounting machine.

In the surface-mount air-core coil described above, the cross section ofthe coil body perpendicular to the axis thereof may be formed of twoopposing substantially semicircular sections and substantially straightsections connecting to the substantially semicircular sections. Sincethe coil body has a flattened shape, the coil has a low profile evenwith the same inductance. Therefore, an electronic component having thisair-core coil and a communication apparatus having this air-core coilcan be made to have a low profile.

In accordance with one aspect of the invention, the surface-mountair-coil, comprises:

a cylindrical coil body having a central axis and a nominal outerdiameter, said cylindrical coil being defined by a spirally woundsection of a conductive wire, said section lying between opposite endsof said conductive wire; and

first and second ends of said conductive wire definite first and secondsubstantially straight legs, respectively, each of said legs extendingsubstantially parallel to one another and substantially perpendicular tosaid central axis of said coil body, and outer edge of both of said legslying outside the nominal outer diameter of said coil body, the lengthof each of said legs being greater than the nominal outer diameter ofsaid coil body.

In accordance with another aspect of the present invention, thesurface-mount air-coil, comprises:

a flattened circle coil body having a central axis and cross sectionlying perpendicular to said central axis, said cross section comprisingtwo opposing substantially semicircular sections and first and secondsubstantially straight sections connecting said substantiallysemicircular sections, said first and second straight sections lyingsubstantially parallel to one another, said flattened circle coil bodybeing defined by a wound section of a conductive wire lying betweenfirst and second ends of said conductive wire; and

said first and second ends of said conductive wire defining first andsecond substantially straight legs, respectively, each of said legsextending substantially parallel to one another and to said straightsections, said second straight sections lying between said firststraight sections and said legs, the nominal distance from said firstsection to said second section being less than the distance from saidfirst section to said legs.

In accordance with another aspect of the invention, the inventioncomprises:

(a) a circuit board;

(b) a first surface-mount air-coil mounted on said circuit board, saidfirst air-coil comprising:

(1) a cylindrical coil body having a central axis and a nominal outerdiameter, said cylindrical coil body being defined by a spirally woundsection of a conductive wire, said section lying between opposite endsof said conductive wire; and

(2) first and second ends of said conductive wire defining first andsecond substantially straight legs, respectively, each of said legsextending substantially parallel to one another and substantiallyperpendicular to said central axis of said coil body, an outer edge ofboth of said legs lying outside the nominal outer diameter of said coilbody, the length of each of said legs being greater than said nominalouter diameter of said coil body; and

(c) A second surface-mount air-coil mounted on said circuit board, saidsecond air-coil comprising;

(1) a flattened circle coil body having a central axis and cross sectionlying perpendicular to said central axis, said cross section comprisingtwo opposing substantially semicircular sections and first and secondsubstantially straight sections connecting said substantiallysemicircular sections, said first and second straight sections lyingsubstantially parallel to one another, said flattened circle coil bodybeing defined by a wound section of a conductive wire lying betweenfirst and second ends of said conductive wire; and

(2) said first and second ends of said conductive wire defining firstand second substantially straight legs, respectively, each of said legsextending substantially parallel to one another and to said straightsections, said second straight sections lying between said firststraight sections and said legs, the nominal distance from said firstsection to said second section being less than the distance from saidfirst section to said legs.

Other features and advantages of the present invention will becomeapparent from the following description of the invention which refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevation of a surface-mount air-core coil according to afirst embodiment of the present invention.

FIG. 2 is a side view illustrating a condition in which thesurface-mount air-core coil shown in FIG. 1 is mounted on a circuitboard.

FIG. 3 is a plan of a package tape into which the surface-mount air-corecoils shown in FIG. 1 are accommodated.

FIG. 4 is a side view of the package tape shown in FIG. 3.

FIG. 5 is an elevation of a surface-mount air-core coil according to asecond embodiment of the present invention.

FIG. 6 is a side view illustrating a condition in which thesurface-mount air-core coil shown in FIG. 5 is mounted on a circuitboard.

FIG. 7 is an elevation of a surface-mount air-core coil according to athird embodiment of the present invention.

FIG. 8 is a perspective view of an electronic component according to anembodiment of the present invention.

FIG. 9 is an electric equivalent circuit diagram of the electroniccomponent shown in FIG. 8.

FIG. 10 is a partial perspective view of a communication apparatusaccording to an embodiment of the present invention.

FIG. 11 is an electric circuit block diagram of the communicationapparatus shown in FIG. 10.

FIG. 12 is an elevation of a conventional surface-mount air-core coil.

FIG. 13 is a side view illustrating a condition in which thesurface-mount air-core coil shown in FIG. 12 is mounted on a circuitboard.

FIG. 14 is a perspective view of a package tape into which thesurface-mount air-core coils shown in FIG. 12 are accommodated.

FIG. 15 is a side view illustrating a condition in which thesurface-mount air-core coil shown in FIG. 12 is erroneously mounted on acircuit board.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A surface-mount air-core coil, an electronic component having thisair-core coil, and a communication apparatus having this air-core coilaccording to embodiments of the present invention will be describedbelow by referring to the accompanying drawings. In each embodiment, thesame symbols are assigned to the same components or the same portions.

As shown in FIG. 1 and FIG. 2, a surface-mount air-core coil 10according to a first embodiment is made from one conductive wire 1covered with heatproof resin such as polyurethane, polyester, orpolyamide, and has a coil body 2 and mount legs 31 and 32.

The coil body 2 is formed by winding the conductive wire 1 spirally in aplurality of turns except for both ends thereof, and is a set of wheels21-24 each of which is formed by one turn of the wire. The coil body 2has a circular cross section (shape of the wheels 21-24) perpendicularto its axis. The height H₂ and the width L₂ of the coil body 2 are equalto the outer diameter of the coil body 2.

The mount legs 31 and 32 are formed by folding both ends of theconductive wire 1 horizontally toward the inside in the directionperpendicular to the axis of the coil body 2. The lower surfaces 31a and32a of the mount legs 31 and 32 are positioned lower than the lowersurface 2a of the coil body 2 with an offset D of about 0.1 to 0.3 mm.The horizontal portions of the mount legs 31 and 32 are formed such thatthe length L₁ thereof is almost equal to the width L₂ of the coil body2. Therefore, the height H of the coil 10 is the sum of the height H₂ ofthe coil body 2 and the offset D. The width L of the coil 10 is equal tothe width L₂ of the coil body 2.

At portions from the tips of the mount legs 31 and 32 to almost theupper ends, resin film is removed to allow mounting, and preliminarysoldering is applied to portions 11 and 12 to improve solderability forreflow soldering. Ends 11a and 12a of the soldered portions 11 and 12are positioned between the top A of the coil body 2 and the bent parts Bof the mount legs 31 and 32. It may be unnecessary to apply preliminarysoldering. Alternatively, solder plating, tin plating, or flux film maybe applied to the portions 11 and 12, instead of preliminary soldering.

The air-core coil 10 having the above structure is mounted on a circuitboard 4 provided with solder paste by reflow soldering by the use of thedrawing nozzle of an automatic mounting machine (not shown). Even if theouter diameters of the wheels 21 to 24 vary due to manufacturing errors,since the lower surfaces 31a and 32a of the mount pegs are disposedlower than the lower surface of the wheels 21 to 24, the lower surfaces31a and 32a of the mount legs positively contact with the circuit board4. Therefore, the coil 10 is mounted on the circuit board 4 withoutproblems such as defective soldering, soldering prevention, or thetombstone phenomenon.

The characteristics, including inductance, of the coil 10 correspond tothe outer diameter (equal to the height H₂ and the width L₂) of the coilbody 2. The height H₂ of the coil body 2 differs according to desiredcharacteristics. When a plurality of coils 10 having slightly differentcharacteristics are provided, the height H₂ of the coil body 2 in eachcoil is different. The heights H₂ of these coils 10 can be set equal,however, by adjusting the offset D.

Therefore, when the heights of these coils 10 are matched to the depthH₃ of the pockets 52 of a package tape 5 having pilot holes 51 shown inFIG. 3 and FIG. 4, such as an emboss-type and paper-tape-type packagetape, even if the package tape 5 has the pockets 52 with a fixed depthH₃, the coils 10 are conveyed without rotating upside-down. Therefore,these coils 10 are mounted on the circuit board 4 without producingmounting defects. In other words, the coils 10 having differentcharacteristics can be transported only by the use of the package tape 5having fixed dimensions without manufacturing package tapes havingpockets whose sizes correspond to the characteristics of the coils 10.

As shown in FIG. 5 and FIG. 6, a surface-mount air-core coil 20according to a second embodiment is provided with mount legs 33 and 34instead of the mount legs 31 and 32 of the coil 10 shown in FIG. 1.

The mount legs 33 and 34 are formed by folding both ends of a conductivewire 1 horizontally toward the inside in the direction perpendicular tothe axis of a coil body 2 with a fold angle θ being set to an acuteangle. The lower surfaces 33a and 34a of the mount legs 33 and 34 arepositioned lower than the lower surface 2a of the coil body 2. Thelength L₁ of the mount legs 33 and 34 are longer than the width L₂ ofthe coil body 2.

With the mount legs 33 and 34 being provided, the width L of the coil 20is equal to the length L₁ of the mount legs 33 and 34. When a pluralityof types of coils 20 having slightly different characteristics aremanufactured, even if the widths L₂ of the coil bodies 2 differ, thelength L₁ of the mount legs 33 and 34 of each coil is adjusted to setall the widths L of the coils 20 equal. Therefore, the width L of eachcoil 20 can be matched to the width L₃ of the pockets 52 of the packagetape 5 (see FIG. 3). Consequently, when the coils 20 are accommodatedinto the package tape having fixed dimensions and are transported, thecoils 20 are prevented from moving, and taking out thereof does notbecome difficult.

As shown in FIG. 7, a surface-mount air-core coil 30 according to athird embodiment is provided with a coil body 25 having aflattened-circular cross section perpendicular to the axis of the coilbody, instead of the coil body 2 of the coil 20 shown in FIG. 5.

The cross section perpendicular to the axis of the coil body 25 isformed of two semicircular portions 26a and 26b and two straightportions 27a and 27b. The opposing semicircular portions 26a and 26b areconnected by the straight portions 27a and 27b at the upper ends and thelower ends to form a flattened circle.

Since the coil body 25 is set to have a low profile with the outerdiameter thereof being almost maintained, a flattened low-profileair-core coil can be manufactured even with the same inductance. In thepresent embodiment, the coil 30 may be manufactured such that the lengthL₁ of the mount legs 33 and 34 is equal to the width L₂ of the coil body25. In this case, the width L of the coil 30 becomes equal to the widthL₂ of the coil body 25.

An electronic component having the surface-mount air-core coil 20 shownin FIG. 5 according to a fourth embodiment will be described below bytaking as an example an antenna multiplexing filter used for a mobilecommunication apparatus such as an automobile phone and a portablephone.

As shown in FIG. 8, an antenna multiplexing filter 100 is formed of acircuit board 101, dielectric resonators 102, 103, and 104 mounted onthe circuit board 101, a ceramic substrate 105, a square capacitor 106,and an air-core coil 20. The air-core coil 20 can be mounted on thecircuit board 101 without any problems, such as defective soldering,soldering prevention, and the tombstone phenomenon. In some cases, aprotective case covers the electrically functional devices 102 to 106and 20 mounted on the circuit board 101 to protect them from theoutside. The circuit board 101 is made from a dielectric material suchas resin or ceramic. Circuit conductors (not shown) are formed on thesurface of the circuit board 101.

In the dielectric resonators 102, 103, and 104, which are known, almostrectangular-parallelepiped dielectric blocks 102a to 104a are providedwith outer conductors 102b to 104b at their outer surfaces and are alsoprovided at their centers with resonator holes 102c to 104c having axesparallel to the longitudinal directions of the blocks. The ceramicsubstrate 105 is provided with two capacitive electrodes 105a and 105bon its surface. The dielectric resonators 102 and 103 are electricallyconnected to the capacitive electrodes 105a and 105b, respectively, ofthe ceramic substrate 105 through connecting terminals 107a and 107bfitted into the resonator holes 102c and 103c, respectively. Thedielectric resonator 104 is electrically connected to one of thecapacitive electrodes of the square capacitor 106 through a connectingterminal 107c fitted into the resonator hole 104c.

The antenna multiplexing filter 100 with the above structure has anelectric equivalent circuit shown in FIG. 9. In FIG. 9, C1, C2, and C3indicate capacitors generated among circuit conductors provided on thecircuit board 101. C6 indicates a capacitor generated between the twocapacitive electrodes 105a and 105b of the ceramic substrate 105. C5indicates a capacitor generated between the capacitive electrode 105aand the circuit conductors on the circuit board 101. C7 indicates acapacitor generated between the capacitive electrode 105b and thecircuit conductors on the circuit board 101.

In this antenna multiplexing filter 100, a transmission signal sent froma transmission circuit system (not shown) to a transmission electrode Txis output from an antenna electrode ANT through the resonator 104. Asignal received from the antenna electrode ANT is output to a receivingcircuit system (not shown) from a receiving electrode Rx through theresonators 102 and 103.

A communication apparatus having the surface-mount air-core coil 20shown in FIG. 5, according to a fifth embodiment will be described belowby taking a portable phone as an example. FIG. 10 shows an RF section ofa portable phone 120. As shown in FIG. 10, an antenna element 122, anantenna multiplexing filter (duplexer) 123, a capacitor 124, an air-corecoil 20, and other parts are mounted on a circuit board 121. Theair-core coil 20 can be mounted on the circuit board 121 without anyproblems such as defective soldering, soldering prevention, and thetombstone phenomenon. This air-core coil 20 is used for adjusting thephase of the antenna element 122. In FIG. 10, there are shown circuitconductors 125 and 126 for signals, which are provided on the uppersurface of the circuit board 121, and a circuit conductor 127 for theground.

FIG. 11 is an electric equivalent circuit block diagram of the RFsection of the portable phone 120 having the above structure. In FIG.11, there are shown a transmission isolator 131, a transmissionamplifier 132, an interstage transmission bandpass filter 133, atransmission mixer 134, a receiving amplifier 135, an interstagereceiving bandpass filter 136, a receiving mixer 137, avoltage-controlled oscillator (VCO) 138, and a local bandpass filter139.

A surface-mount air-core coil, an electronic component having thisair-core coil, and a communication apparatus having this air-core coilaccording to the present invention are not limited to those described inthe above embodiments. They can be modified in various ways within thescope of the invention.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled man in the art that the forgoing and other changes in formand details may be made therein without departing from the spirit of theinvention.

What is claimed is:
 1. A surface-mount air coil formed of a singleconductive wire and having a height and a length, said air coilcomprising:first and second substantially straight legs defined byopposite ends of said conductive wire, each of said legs having alowermost edge lying in a first plane; and a cylindrical coil bodydefined by a spirally wound section of said conductive wire, said coilbody having a nominal diameter and a central axis lying parallel to andspaced from said first plane, said coil body having a height as measuredbetween uppermost and lowermost outer peripheries of said coil body asviewed along a second plane running perpendicular to said first planeand through said central axis, said coil body having a length asmeasured between leftmost and rightmost outer peripheries of said coilbody as viewed along a third plane which extends parallel to said firstplane and through said central axis; said lowermost outer periphery ofsaid coil body being located above and spaced apart from said firstplane whereby said height of said air coil as measured along said secondplane is greater than said height of said coil body; and each of saidlegs straddling opposite sides of said coil body as viewed along saidfirst plane such that said length of said air coil as measured alongsaid first plane is greater than the length of said coil body.
 2. Asurface-mount air-coil according to claim 1, wherein said coil body iscovered with resin film.
 3. A surface-mount air-coil according to claim2, wherein said coil body is covered with resin film.
 4. A surface-mountair-coil according to claim 1, wherein said coil body is defined by aplurality of individual coils and the diameter of at least some of saidindividual coils varies slightly from those of at least one of the otherindividual coils, but the distance from the center of said coil body tosaid legs as measured along a radius of said coil body is greater thanthe maximum radius of all of said individual coils.
 5. A surface-mountair coil according to claim 1, wherein said first leg is coupled to afirst end of said coil body by a first connector section of saidconductive wire which extends along a straight line which is oblique tosaid first plane and is coupled to said first leg at a position to theleft of said leftmost outer periphery of said coil body, and said secondleg is coupled to a second end of said coil body by a second connectorsection of said conductive wire which extends along a straight linewhich is oblique to said first plane and is coupled to said second legat a position to the right of said rightmost outer periphery of saidcoil body.
 6. A device, comprising:a) a circuit board; b) at least oneelectronic component mounted on said circuit board; and c) asurface-mount air-coil mounted on said circuit board, said air-coilformed of a single conductive wire and having a height and length, saidair coil comprising:1) first and second substantially straight legsdefined by opposite ends of said conductive wire, each of said legshaving a lowermost edge lying in a first plane; and 2) a cylindricalcoil body defined by a spirally wound section of said conductive wire,said coil body having a nominal diameter and a central axis lyingparallel to and spaced from said first plane, said coil body having aheight as measured between uppermost and lowermost outer peripheries ofsaid coil body as viewed along a second plane running perpendicular tosaid first plane and through said central axis, said coil body having alength as measured between leftmost and rightmost outer peripheries ofsaid coil body as viewed along a third plane which extends parallel tosaid first plane and through said central axis; 3) said lowermost outerperiphery of said coil body being located above and spaced apart fromsaid first plane whereby said height of said air coil as measured alongsaid second plane is greater than said height of said coil body; and 4)each of said legs straddling opposite sides of said coil body as viewedalong said first plane such that said length of said air coil asmeasured along said first plane is greater than the length of said coilbody.
 7. A device according to claim 6, wherein said coil body iscovered with resin film.
 8. A device according to claim 7, wherein saidlegs are not covered with resin film.
 9. A device according to claim 6,wherein said coil body is defined by a plurality of individual coils andthe diameter of at least some of said individual coils varies slightlyfrom those of at least one of the other individual coils, but thedistance from said central axis of said coil body to said legs asmeasured along a radius of said coil body is greater than the maximumradius of all of said individual coils.
 10. A device according to claim6, wherein said first leg is coupled to a first end of said coil body bya first connector section of said conductive wire which extends along astraight line which is oblique to said first plane and is coupled tosaid first leg at a position to the left of said leftmost outerperiphery of said coil body, and said second leg is coupled to a secondend of said coil body by a second connector section of said conductivewire which extends along a straight line which is oblique to said firstplane and is coupled to said second leg at a position to the right ofsaid rightmost outer periphery of said coil body.